JP3326140B2 - Magnesium alloy die casting and die casting products - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for die-casting magnesium alloy and a die-cast product, and more particularly, the present invention relates to a method for casting a magnesium alloy melt by using a cold-chamber type die-casting machine. Ensure the filling properties,
The present invention relates to a die casting method for controlling the surface properties, hot cracks, shrinkage cracks, and shrinkage cavities of a cast product to produce a high-quality magnesium die casting product at a lower cost, and a die casting product obtained by the die casting method.

[0002]

2. Description of the Related Art In the automotive industry, there is a need for lightweight materials for improving fuel efficiency, and for home electric appliances and the like, there is a need for lightweight materials for improving portability. Has been used. But,
Resin materials are generally difficult to recycle and pose a problem in terms of global environmental protection, whereas metal materials are generally easy to recycle, making housing for home appliances, especially portable products , for example, notebook personal computers, cellular phones, digital video cameras, MD Walkman, cameras of the portable product of the housing, the magnesium-based material manufacturing material of a resin material various cases parts of automobiles, light metal of aluminum-based material or the like In particular, in the trend of lightness, thinness and small size, the lightest magnesium-based material, which has the rigidity as a metal but has the lowest density among practical lightweight metals, has been attracting attention, and is attracting attention as a material for automobiles or portable home appliances. Therefore, a product having a portion having a thickness of 1.5 mm or less is required.

Conventionally, a die casting method is generally used as a method for producing a magnesium alloy product, and in particular, a hot chamber die casting method is widely used. However, it is possible to easily switch from a magnesium alloy material to an aluminum alloy material that is cheaper than a magnesium alloy, using the casting device itself introduced as a dedicated die casting machine for die-casting a magnesium alloy, or Because it is possible to divert a conventional aluminum alloy die casting machine instead of introducing a dedicated die casting machine, various new alloy types that are difficult to cast with a hot chamber type die casting machine are also introduced. Since it has been developed and used, it is desired to establish a casting method of a magnesium alloy in a cold chamber die casting method.

[0004]

A problem that arises when a magnesium alloy is to be cast using a cold chamber type die casting machine is that a magnesium alloy generally has a low latent heat of solidification and solidifies quickly, so that a molten metal must flow. There are states to be described. This state is particularly the case of portable home appliances and the like, for example, notebook personal computers,
Mobile phones, digital video cameras, MD walkmans,
This is a problem in the manufacture of thin parts of housings such as cameras and projectors.

Further, there is a magnesium alloy to which silicon, a rare earth element, calcium or the like is added in order to improve the creep characteristics particularly at high temperature and room temperature. However, these elements are active and easily generate oxides. A compound is formed in the grain boundary portion, so that hot cracks and shrinkage cracks are liable to occur. This also poses a problem when a die-cast product is produced from such an alloy by using a cold-chamber die-casting machine.

In order to solve these problems and problems when a cold chamber type die casting machine is used for manufacturing a magnesium alloy die casting product, conventionally, measures such as increasing the mold temperature and increasing the injection speed have been used. However, it was not possible to achieve the desired results, and in some cases, casting with a cold chamber type die casting machine was abandoned.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and the present invention has been made to secure the fluidity of a magnesium alloy melt in casting of a magnesium alloy die cast product using a cold chamber type die casting machine. Filling, surface properties of cast products, hot cracks and shrinkage cracks, shrinkage cavities are controlled, and a die casting method for producing a high-quality magnesium die casting product at a lower cost and a die casting product obtained by the die casting method are provided. The challenge is to provide.

[0008]

The present inventors have made various studies to achieve the above-mentioned object, and as a result, when using a cold-chamber die-casting machine, it is necessary to use a cold-chamber-type die-casting machine at the gate portion. It was first found that it is important to maintain the temperature of the molten magnesium alloy at a certain value or higher (590 ° C. or higher).

In addition, it is necessary to raise the temperature of the molten metal in the molten metal holding pot (molten metal holding furnace) in order to secure the temperature of the molten metal at the gate portion above the predetermined value. It is necessary to avoid exceeding 750 ° C from the temperature, and further, if the degree of cooling of the molten metal in the middle of the process from the molten metal holding pot to the gate is large,
Part of the magnesium alloy melt begins to solidify in the sleeve, which also impairs the fluidity of the melt and increases the degree of oxidation in the course of the melt. the difference between the melt temperature kept within a certain temperature Sa以in a particular manner as the hot water supply system
Used, the sleeve part is made of a specific material and has a specific thickness or more
So that the sleeve is heated and maintained above a specific temperature.
And finding that it is necessary to equity, thereby completing the present invention.

That is, in the magnesium alloy die casting method of the present invention, when a magnesium alloy die casting product is cast using a cold chamber type die casting machine, the temperature of the magnesium alloy melt at the gate of the cold chamber type die casting machine is increased. Is maintained at 590-720 ° C, and the magnesium alloy melt is coaled from the melt holding pot.
Hot water supply to sleeve of de-chamber type die casting machine
As a system, siphon system, mega pump system, decompression or
Cold pressurized pump or electromagnetic pump
The thermal conductivity of the sleeve part of the chamber type die casting machine
0.085 cal / cm · s · ° C or less and thickness
10 mm or more.
A magnesium alloy having a portion having a thickness of 1.5 mm or less by heating and maintaining the temperature at 0 ° C. or more and maintaining a temperature difference between the temperature of the molten metal in the molten metal holding pot and the temperature of the molten metal at the gate portion at 60 K or less. It is characterized by casting die-cast products.

Further, the die cast product of the present invention is a magnesium alloy die cast product which can be produced by the above-mentioned die casting method. In the present invention, a die-cast product includes a die-cast component.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The type of magnesium alloy that can be used in the die casting method and the die cast product of the present invention, the operating conditions of the cold chamber type die casting machine, the configuration of the cold chamber type die casting machine, etc. will be described in detail below. I do.

The magnesium alloy that can be cast by the die casting method of the present invention may be any magnesium alloy that can be die cast. For example, MD1A, MD1B, MD1D, M1
D2A, MD2B, MD3A and the like can be used.

However, when a magnesium alloy die-cast product having sufficient strength even at a high temperature up to about 523 K, which is required for weight reduction of automobile engine parts and the like, i) aluminum 1 to 10% by weight; ii) Rare earth element 0.2 to 5% by weight, calcium 0.02
-5% by weight and at least one selected from the group consisting of silicon 0.2-10% by weight; and iii) a magnesium alloy containing manganese 1.5% by weight or less, with the balance being magnesium and unavoidable impurities. Preferably, it is used.

[0015] The die casting method of the present invention has a constitutional requirement that a magnesium alloy die casting product is cast using a cold chamber type die casting machine. When a cold chamber type die casting machine is used, the flow of the molten magnesium alloy is reduced. The gate of a cold-chamber die-casting machine is required to ensure the filling property, control the filling property, the surface properties of the cast product, hot cracks, shrinkage cracks, shrinkage cavities, and manufacture high-quality magnesium die-cast products at lower cost. Temperature of the magnesium alloy at 590
It is important to keep the temperature above ℃.

In order to maintain the temperature of the molten metal at the gate at 590 ° C. or higher, it is necessary to raise the temperature of the molten metal in the molten metal holding pot (melt holding furnace).
Must be avoided. In addition, cooling is inevitable while the molten magnesium alloy moves from the molten metal holding pot to the gate, and the higher the temperature of the molten metal in the molten metal holding pot, the greater the degree of cooling of the molten metal. Extra equipment and extra costs are required to reduce the degree of cooling of the molten metal. For this reason, the temperature of the magnesium alloy melt at the gate is 720
It is realistic to keep the temperature below ° C. Therefore, in the die casting method of the present invention, the temperature of the molten magnesium alloy at the gate of the cold chamber die casting machine is maintained at 590 to 720 ° C.

Further, when the degree of cooling of the molten metal in the middle of the process from the molten metal holding pot to the gate portion is large, a part of the magnesium alloy melt starts to solidify in the middle of the process and in the sleeve. In addition, since the degree of oxidation in the course of the process becomes large, the temperature of the molten metal in the molten metal holding pot and the temperature of the molten metal in the gate portion are controlled in order to prevent such a defect from occurring. 105K difference
, Preferably within 60K.

As a result of examining means for realizing a reduction in the degree of cooling of the molten metal in the middle of the process from the molten metal holding pot to the gate section in actual operation, an automatic hot water supply system is adopted as a hot water supply / pouring system. Thus, it has been found that the molten metal can be transported to a position directly above the sleeve at the same temperature as the molten metal in the molten metal holding pot. As such an automatic hot water supply system, a siphon system, a mega pump system, a decompression or pressurization pump system, or an electromagnetic pump system can be adopted. These automatic hot water supply systems are known, and those known automatic hot water supply systems can be employed as they are.

In order to reduce the degree of cooling of the molten metal in the middle of the process from the molten metal holding pot to the gate, the sleeve of the cold chamber type die casting machine is required to have a thermal conductivity of 0.085 cal / cm · s · ° C. or less. The material is made to have a thickness of 10 mm or more to enhance the heat retention in the sleeve portion, and the sleeve portion is heated and held at 100 ° C. or more, preferably 250 ° C. or more, so that the molten metal in the sleeve portion Preferably, the temperature is maintained.

As such a sleeve material, SKD61 is used.
Hot tool steel (thermal conductivity 0.085 cal / cm · s)
・ ℃), or in order to reduce the thermal conductivity of the sleeve as a whole, these hot tool steels are sprayed with ceramics with low thermal conductivity, composites of ceramics and metal, or the like. T on hot tool steel by CVD etc.
iC, TiCN, CrC, W ₂ C, TiN, TiCr
With a coating layer of N, CrN, etc., SiN,
Examples thereof include ceramics such as Sialon, ZrB ₂ , Al ₂ O ₃ , and SiC, and composites of the above ceramics on an iron-based or titanium-based substrate.

In order to reduce the degree of cooling of the molten metal in the middle of the course from the molten metal holding pot to the gate, the runner is maintained at 150 degrees for maintaining the temperature of the molten metal in the runner from the gate to the gate. C., preferably 180-350.degree. C. while maintaining excellent heat retention at the same time as graphite, BN, water glass,
It is also effective to apply at least one selected from the group consisting of mica, silica gel, magnesium hydroxide and magnesium oxide, or to apply a release agent to which at least one of these is added.

In the die casting method of a magnesium alloy of the present invention, by adopting the above-mentioned conditions, the flowability of the molten magnesium alloy is ensured, and the filling property, the surface properties of the cast product, hot cracking, shrinkage cracking, shrinkage, etc. The nest can be controlled to produce a high-quality magnesium die-cast product at a lower cost, and is effective for thin-wall casting, especially for thin-wall casting of 1.5 mm or less, and casting of alloys containing silicon, rare earth elements, and calcium.

[0023]

The present invention will be specifically described below based on examples and comparative examples. Examples 1 and 2 and Comparative Examples 1 to 3 AZ91 (Mg-9Al-0.
7Zn-0.2Mn) alloy was melted, and the temperature (A) of the molten metal in the molten metal holding pot was maintained as shown in Table 1.
Cold chamber type die casting machine made by Ube 65
The material shown in Table 1 (MC is a metal ceramic obtained by combining SiN ceramics on a titanium alloy) and the thickness shown in Table 1 were used as the sleeve of the die casting machine. Was heated to the temperature shown in Table 1. A siphon method is used as an automatic hot water supply system from the molten metal holding pot to the sleeve, and when the siphon tube is heated, the first method is used.
Heated to the temperature shown in the table. Further, the melt temperature at the inlet of the sleeve and the melt temperature (B) at the gate were measured. The measurement results are as shown in Table 1. Temperature difference between the temperature of the molten metal in the molten metal holding pot and the temperature of the molten metal at the gate (A-
B) is also shown in Table 1.

The mold temperature is 250 ° C., the air pressure in the mold during die casting is 40 mmHg, the filling speed into the cavity is 5/100 seconds, and the pressure increase after filling is 500.
kgf / cm ^2, and a talc-based release agent (manufactured by Hanano Shoji Co.) is applied to the inner surface of the mold to obtain an A4 size (210 mm ×
297mm), depth 10mm, thickness 1mm (partly 0.8
mm part) was cast. The casting results were as shown in Table 1.

[0025]

[Table 1]

Examples 3 to 10 Using a closed melting furnace, alloy 1 = AZ91 (Mg-9Al-0.7Zn-0.2
Mn), alloy 2 = Mg-5Al-2Ca-2RE-0.2Mn, alloy 3 = Mg-5Al-4Ca-0.2Mn, alloy 4 = Mg-5Al-4RE-0.2Mn, alloy 5 = Mg-5Al -8Si-0.2Mn, Alloy 6 = Mg-9Al-2RE-1Si-0.05Ca
-0.02Mn, Alloy 7 = Mg-5Al-0.5RE-0.1Si-0.
1Ca-0.02Mn and alloy 8 = Mg-2Al-2Ca-0.2Mn were melted, and the temperature (A) of the molten metal in the molten metal holding pot was maintained as shown in Table 2. .

A cold chamber type die casting machine was used, a 650 t machine made by Ube, a sleeve of the material and thickness shown in Table 2 was used as a sleeve of the die casting machine, and the sleeve was heated to a temperature shown in Table 2. A siphon system was used as an automatic hot water supply system from the molten metal holding pot to the sleeve, and the siphon tube was heated to the temperature shown in Table 2. Further, the melt temperature at the inlet of the sleeve and the melt temperature (B) at the gate were measured. The measurement results are as shown in Table 2. The temperature difference (AB) between the temperature of the molten metal in the molten metal holding pot and the temperature of the molten metal at the gate is also second.
It is shown in the table.

The mold temperature is set to 200 ° C., the air pressure in the mold during die casting is set to 50 mmHg, the filling speed to the cavity is set to 5/100 seconds, and the pressure increase after filling is 500.
kgf / cm ^2, and a talc-based mold release agent (manufactured by Hanano Shoji Co., Ltd.) is applied to the inner surface of the mold to obtain an automobile part 300
A box-shaped prototype having a size of 300 mm x 180 mm and a thickness of 3 mm was cast. The casting results were as shown in Table 2.

[0029]

[Table 2]

[0030]

According to the present invention, the temperature of a molten metal from a molten metal holding pot to a gate portion is controlled in casting of a magnesium alloy when using a cold chamber type die casting machine, which is demanded in a wide range of industries mainly in the automobile industry and the home appliance industry. By doing so, the fluidity of the magnesium alloy melt is secured,
Filling properties, surface properties of cast products, hot cracks, shrinkage cracks, shrinkage cavities were controlled, and it became possible to manufacture high-quality magnesium products at lower cost.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C22C 23/02 C22C 23/02 (56) References JP-A-7-9108 (JP, A) Castings, Japan, Japan Foundry Association, December 25, 1995, Vol. 67, No. 12, pp. 924-928 '86 Magnesium Manual, Japan, Magnesium Commission, November 5, 1986, pp. 85-89 AI-Aru, Japan, Stock Co., Ltd., April 28, March-April 1992, Merger, pp. 23-32 Materia, Japan, The Japan Institute of Metals, April 20, 1999, vol. 38 No. 4, 286, 288-289 Magnesium Committee, Magnesium Handbook, Japan, Japan Light Metal Association, June 13, 1975, p. 124, 1992 Japan Die Casting Conference, Japan, Japan Die Casting Association, September 1992 1, 259-260, 1984 Japan Die Casting Conference, Japan, Japan Die Casting Association, October 23, 1984, p. 70 (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 17 / 20 B22D 17/30

Claims (3)

(57) [Claims] When casting a magnesium alloy die cast product using a cold chamber type die casting machine,
The temperature of the molten magnesium alloy at the gate of the cold chamber die casting machine is maintained at 590-720 ° C,
Cold melt magnesium alloy from molten metal holding pot
System for supplying hot water to the sleeve of a chamber die casting machine
As siphon system, mega pump system, decompression or pressurization
Use cold pump or electromagnetic pump
The thermal conductivity of the sleeve part of a member-type die-casting machine is set to 0.
085 cal / cm · s · ° C or less and thickness 10
mm or more, and the sleeve portion is kept at 100 ° C.
A die-cast product of a magnesium alloy having a portion having a wall thickness of 1.5 mm or less by heating and holding as described above, and maintaining the temperature difference between the temperature of the melt in the molten metal holding pot and the temperature of the melt at the gate portion at 60 K or less. Die casting of magnesium alloys, characterized by casting. 2. As magnesium alloy, i) 1 to 10% by weight of aluminum, ii) 0.2 to 5% by weight of rare earth element, 0.02% of calcium
-5% by weight and at least one selected from the group consisting of silicon 0.2-10% by weight; and iii) a magnesium alloy containing manganese 1.5% by weight or less, with the balance being magnesium and unavoidable impurities. die casting process according to claim 1 Symbol placement which comprises using. Die casting of 3. A magnesium may be prepared by the claims 1 or 2 die casting method described alloys.